A radiotelephone normally comprises a screen and an alphanumeric keypad where a user may input information to the radiotelephone using the alphanumeric keypad and simultaneously display that information on the screen. The size of the radiotelephone is primarily limited by the size of the screen and alphanumeric keypad. It is desirable for the radiotelephone to be compact so that the user may place the radiotelephone in a pocket. While both the screen and the keypad may be reduced in size, the screen must be large enough so that characters displayed on it are large enough to be read by the user. The alpha numeric keypad must be large enough so that the user is able to input data without inadvertently activating two keys at the same time.
It is a desirable feature of a radio telephone that the screen is large enough to recognise the data which has been input by the user with the alphanumeric keypad and to allow the user to use other applications on the radio telephone, the playing of games being one such application. It is therefore undesirable that the screen size be reduced. The dimensions of a radiotelephone are limited by the screen and keypad unless an alternative form of user input to replace the alphanumeric keypad is made available.
The Nokia 7110 included a roller key described in UK patent EP0901262. The rotational movement of the key was detected using a mechanical conductive switch which added to the dimension requirements of the device.